Accepted Manuscript

Electrical and Magnetic Properties of (SbLi)1/2Fe2/3Mo1/3O3 Multiferroic Mate-rial

Suhel Ahmed, Subrat Kumar Barik

PII: S0925-8388(14)02690-5DOI: http://dx.doi.org/10.1016/j.jallcom.2014.11.047Reference: JALCOM 32596

To appear in: Journal of Alloys and Compounds

Received Date: 1 August 2014Revised Date: 3 November 2014Accepted Date: 7 November 2014

Please cite this article as: S. Ahmed, S.K. Barik, Electrical and Magnetic Properties of (SbLi)1/2Fe2/3Mo1/3O3

Multiferroic Material, Journal of Alloys and Compounds (2014), doi: http://dx.doi.org/10.1016/j.jallcom.2014.11.047

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customerswe are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, andreview of the resulting proof before it is published in its final form. Please note that during the production processerrors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

1

Electrical and Magnetic Properties of (SbLi)1/2Fe2/3Mo1/3O3 Multiferroic Material

Suhel Ahmed, Subrat Kumar Barik*

Department of Physics

National Institute of Technology, Silchar, Assam-788010, India

Abstract:

Synthesis and characterization of lithium and molybdenum modified antimony ferrite

(SbLi)1/2Fe2/3Mo1/3O3 were carried out using solid-state reaction techniques. The preparation

conditions and mass loss of the homogeneous mixture of required ingredients were decided

based on thermal analysis (TGA). The formation of single-phase compound was confirmed

by preliminary structural analysis using X-ray diffraction data. Electric properties of the

material were studied in a wide temperature range (30-500 ºC) at different frequencies (100

Hz-1 MHz) using impedance spectroscopy technique. The dc conductivity was found to obey

Arrhenius relation suggesting the material to be of NTCR type. The activation energy

calculated from the dc conductivity curve for grain and grain boundary effect is 0.60 and 0.47

eV respectively. The Jonscher’s universal power law governs the nature of ac conductivity of

the material. Remnant polarization was found to be 0.86 (μC/cm2). The magnetic

measurements revealed weak remnant magnetization (0.01516 emu/g).

Keywords: Solid-state reaction; Thermal analysis; X-ray diffraction; Impedance

spectroscopy

___________________________________________________________________________

*Corresponding author's e-mail: subrat.nits@gmail.com

Tel.: +91-3842-242914; Fax: +91-3842-224797

Both the author's have equal contribution in this paper.

2

1. Introduction:

Nowadays multiferroics are found to be very promising and interesting materials because of

their wide industrial applications as multistate memory element, resonance devices,

transducers, actuators, sensors and spintronic devices [1-4]. These materials have the

properties of controlling the electric polarization by the application of magnetic field and vice

versa, commonly known as magnetoelectric coupling. A multiferroic material has at least two

of ferroic properties namely ferroelectric, ferromagnetic or ferroelastic in the same phase of

the material [5].

Among all the single-phase multiferroic materials, BiFeO3 is one of the interesting

compound due to its high Curie temperature (~1100 K) and Neel temperature (~653 K). The

origin of multiferroic properties in BFO is believed due to the presence of 6s lone pair

electrons of Bi3+

which lead to the ferroelectric properties and ferromagnetic is due to

partially field d-orbital of Fe3+

[6]. Absence of large remnant magnetization in BFO is due to

spatially modulated spiral spin structure where as lack of large polarization is due to the

leakage current and low resistance caused by oxygen vacancies and secondary phases.

Several attempts have been made to reduce the above shortcoming by suitable substitutions at

the Bi- and/or Fe-site in the compound. Nalwa et al. enhanced both the remnant polarization

and magnetization of BiFeO3 by suitable substitution in it [1]. Mao et al prepared Bi1-

xErxFe0.95Co0.05O3 where they were able to decrease leakage current, and increase both the

ferroelectric and magnetic properties [7]. Wu et al. reported that due to the both A and B site

substitutions in BiFeO3 by Ba and Nb, the electric and magnetic properties were increased

[8]. It also decreased the loss in the Bi0.8Ba0.2Fe1-xNbxO3 material. Enhancement of ac

conductivity was also reported in (BiNa)1/2(FeV)1/2O3 by Bera et al. [9]. Also Zn and Mn

modified BiFeO3 thin shows much enhanced ferroelectric properties (2Pr~235 μC/cm2)

together with low value of leakage current density [10] where as BiFeO3 thin films of varying

degrees of (111) orientation are grown on SrRuO3-buffered Pt/Tio2/Sio2/Si (100) substrates

by off-axis radio-frequency magnetron sputtering demonstrate much enhanced ferroelectric

behavior (2Pr~197.1 μC/cm2 at 1 kHz) [11]. Thus all the above work both in ceramic and thin

film is confined with BiFeO3 to enhance their ferroelectric and ferromagnetic properties. So

far our knowledge no work has reported to increase the properties of doped or co-doped

SbFeO3. Hence for better understanding and to make SbFeO3 as useful as BiFeO3 material,

we have doped Li in Sb-site and Mo in Fe-site of the prepared material. The reason for taking

Li and Mo ions because of their nearly ionic radius as that of Sb and Fe ions respectively. In

3

this paper we have reported the electric and magnetic properties of a new

(SbLi)1/2Fe2/3Mo1/3O3 (SLFMO) multiferroic material.

2. Experimental

Polycrystalline samples of (SbLi)1/2Fe2/3Mo1/3O3 were prepared by a solid-state reaction

technique using high-purity (≥ 99.9%) carbonates and oxides; Sb2O3, (M/s Loba Chemie Co

Pvt. Ltd.), Li2CO3, MoO3 (M/s SRL Pvt. Ltd.) and Fe2O3 (M/s Merck Pvt. Ltd.) in

stoichiometry ratio. All the precursors were first mixed in an agate mortar and pestle for 2 h

and then in methanol for 2 h. To know the weight loss with temperature and prior information

about the calcinations temperature, the mixed sample was characterized by thermo-

gravimetric analysis (TGA). Based on TGA, the homogeneous powder sample was calcined

at a temperature of 950 ºC for 4 h. After calcinations, XRD of the powder sample was carried

out by using PANalytical XPERT-PRO diffractometer with CuKα radiation (wavelength

λ=1.5405 Å) at a step of 0.01 in the 2θ range (20º-80º) for the confirmation of single

phase multiferroic compound. The process of calcinations and XRD analysis were repeated

till the formation of a single phase of the compound. Polyvinyl alcohol (PVA) was added to

the calcined powder as a binder that was burnt out during high-temperature sintering.

Cylindrical pellets (diameter=13 mm, thickness=2 mm) are made by using a hydraulic press

at a uni-axial pressure of 6x106

N/m2. The pellets were subsequently sintered at an optimized

temperature of 950 ºC for 4 h. For electrical and P-E loop measurements, both the flat

surfaces of the pellets were electroded with high-quality silver paints, and thereafter, the

pellets were kept at 150 ºC for 4 h for the vaporization of moisture, if any. Measurement of

the electrical properties of the sample was carried out with the help of LCR meter (HIOKI Hi

Tester-3532) in a wide range of temperature range (30-500 ºC) at different frequencies (100

Hz-1 MHz). For understanding the magnetic properties of the prepared sample, M-H loop of

the un-silvered pellet was measured with the help of vibrating sample magnetometer (VSM;

Lakeshore 7410).

3. Results and discussion

3.1. Thermal analysis:

Fig.1 shows TGA curve of the un-calcined SLFMO mixture. At the first stage, the weight loss

of 2.7 % was observed at 500 ºC due to the presence of moisture and trapped water in the

4

pores of the mixture. At the second stage (950 ºC) the weight loss of the sample was 19.48 %

which may be due to the decomposition of oxides and carbonates. Above that temperature, no

weight loss was observed which corresponds to the calcinations temperature and accordingly

the sample was calcined at 950 ºC.

3.2. Structural analysis:

The formation of single-phase polycrystalline multiferroic material was confirmed using X-

ray diffraction pattern at room temperature (Fig. 2). The peaks were indexed using a standard

computer program package “POWDMULT” [12]. The calculated and observed values of

lattice spacing for each reflection for different lattice system were compared. The crystal

structure of the prepared material was found to be orthorhombic depending on the best

agreement between dobs and dcal [∑∆d=∑ (dobs-dcal)=minimum]. The least-squares refined unit

cell parameters are: a = 6.6226 Å, b = 10.7984 Å, c = 8.1752 Å having ±0·003 standard

deviation and volume V = 584.64 Å3. By using strong reflection peak (022) of XRD pattern,

the crystallite size of the samples was calculated to be 37 nm from the broadening of

reflections (β1/2) using Scherrer’s equation (Phkl=0.89λ/β1/2cosθ). The calculated value of

tolerance factor for SLFMO is 0.77 which confirmed the distorted perovskite structure.

3.3. Electrical Study

3.3.1. Impedance spectroscopy study

Impedance spectroscopy analysis is one of the finest techniques to understand the grain and

grain boundary effect in materials. Fig. 3 shows Nyquist plots of SLFMO at different

temperatures. From the graph it is observed that the value of Z' decreases with increase in

frequency indicating an increase in ac conductivity of the material. Two semicircular arcs are

observed in all temperature indicating the presence of both grain and grain boundary effect in

the material. The semicircle at high frequency is due to the grain effect usually comprises

with parallel combination of grain resistance (Rg) and capacitance (Cg) where as at low

frequency semicircle is due to grain boundary effect generally represented by parallel

connection of grain boundary resistance (Rgb) and capacitance (Cgb). It is believed that these

compounds lose oxygen during high temperature sintering process according to the relation

5

eVOO 22

12 [13] where

V represent oxygen vacancies with two positive

charges. Again during the time of cooling re-oxidation takes place. This results the different

values of resistance in the grain and grain boundary [14]. The centre of depressed semi-

circles lies below the real axis indicating the presence of non-Debye type behavior in the

material [15]. This non ideal behavior may be due to several factors like grain orientation,

grain size distribution, grain boundaries, atomic defect distribution and stress-strain

phenomena [16]. The departure from ideal Debye behavior justifies the presence of constant

phase element (CPE) in the equivalent circuit representing the electrical response in the

material [17]. CPE is generally represented by CPE(Y) =Ao(jω)n =Aω

n +jBω

n [18] where A=

Aocos(nπ/2) and B=Aosin(nπ/2). Here Ao and n are temperature dependent but frequency

independent term, Ao determines the magnitude of dispersion where as n has a specific value

whether CPE is ideal capacitor (n=1) or a resistor (n=0). The equivalent circuit of SLFMO

for impedance spectrum can be modeled with series connection of two parallel combination

of (i) resistance (grain resistance), capacitance (grain capacitance) and a CPE, with another

parallel combination of (ii) resistance (grain boundary resistance) and capacitance (grain

boundary capacitance) as shown fig. 4. The experimental data is fitted (solid line) using

ZSIMP WIN version 2 software and the values are listed in the Table 1. From the table it is

observed that the both grain and grain boundary resistance decreases with increase in

temperature which suggests negative temperature coefficient of resistance (NTCR) in the

material typical to the semiconducting behavior. Also the value of grain resistance is large in

comparison with grain boundary resistance which may be due to the presence of vacancies

and space charge at the grain boundary [19].

3.3.2. dc conductivity study

The dc conductivity of the material was calculated from the Nyquist plot by using the relation

ζdc=t/RA where R (grain or grain boundary resistance) is calculated from the intercept of the

semicircular arc on the real axis, t and A is the thickness and area of the sample respectively.

Fig. 5 shows the variation of dc conductivity due to the grain and grain boundary effect

respectively with temperature. From the graph, it is revealed that the conductivity increases

with increase in temperature, which again shows NTCR behavior of the material [20]. The

gradual increase in the electrical conductivity with rise in temperature shows a typical

Arrhenius relation; ζdc=ζ0exp [−Ea/KBT], where ζ0 is the pre-exponential term, Ea the

6

activation energy and KB is the Boltzmann constant. The value of activation energy (275-500

ºC) is found to be 0.60 eV and 0.47 eV due to grain and grain boundary effect respectively.

Higher value of activation energy in grain compared to the grain boundary may be due to

larger value of grain resistance compared to grain boundary as shown in table 1. As the

values of activation energy is lower than (~0.70 eV) of second ionization of oxygen

vacancies. Hence first ionization of oxygen vacancies and electron hopping are responsible in

SLFMO for electrical conduction [21, 22].

3.3.3. ac conductivity study

To understand the effect of frequency on the electrical property of the material, ac

conductivity was carried out. The conductivity was calculated from the dielectric data by

using the relation ζac= ωεrε0tanδ, where ε0 is the permittivity in free space and ω is the

angular frequency. Fig. 6 shows the variation of ac conductivity with frequency at different

temperatures. The following conclusion can be drawn from the figure; (i) below 400 ºC there

is a continuous dispersion region without plateau which can be explain with the relation ζ α

ωn and (ii) at a temperature ( ≥ 400 ºC), there is a change in the slope at a particular frequency

known as hopping frequency [23] which increases with increase in temperature .In the

conductivity graph the dispersion region is frequency dependent where as plateau region is

the frequency independent dc conductivity. In this temperature range the conductivity

phenomenon is governed by the Jonscher’s universal power law stated as ζ(ω) = ζdc + A(ω)n,

where ζdc is the dc conductivity, n is temperature dependent exponent (0 ≤ n≤ 1) which

represents the degree of interaction between the lattices with mobile ions, and A determines

the strength of polarizability. By fitting the experimental data with Jonscher’s equation the

values of n are determined which is varied from 0.49 (325 ºC) to 0.14 (500 ºC). The decrease

value of n with rise in temperature suggests the multiple hops of the charge carrier. Further

rise in the conductivity process with increase in temperature is due to the thermally activated

process in the material [24] or may be due to the increased mobility of oxygen vacancies

[21].

3.4. Ferroelectric Study:

Fig. 7 shows the graph of polarization vs. applied electric field of SLFMO at room

temperature. The presence of P-E loop confirmed the ferroelectric nature of the material.

Absence of saturation polarization is possibly due to the leakage current [25]. The leaky

7

features of the material could be connected to oxygen vacancies or valence instability of the

transition metal ion leading to electronic conduction [26]. The remnant polarization of the

material is found to be 0.86 μC/cm2 with saturation polarization (Ps) of 4.67 μC/cm

2 and

coercive filed (Hc) 0.752 kV/cm by an applied voltage of 4 kV/cm. It is interesting to note

that the prepared material has high remnant polarization as compared to those of well-known

multiferroic materials like BiMnO3 [27], Sm and Co modified BiFeO3 [28], Eu doped BiFeO3

[29].

3.5. Ferromagnetic Study:

Fig. 8 shows the variation of magnetization (M) with applied magnetic field (H) up to 15 kOe

at room temperature. Linear dependence of magnetization with applied magnetic field

suggests the antiferromagnetic properties of the material [30, 31]. The value of remnant

magnetization (Mr), saturation magnetization (Ms) and coercive field (Hc) are 0.01516

emu/g, 0.31468 emu/g and 646.254 Oe respectively which is found to be much better as

compared to some known multiferroics such as BiFeO3, Bi1-xHoxFeO3 (x= 0.15 and x= 0.20)

[4, 32, 33]. The value of magnetic moment corresponding to the saturation magnetization is

0.01779 emu. The enhanced values of magnetization may be due to both A & B site doping.

Exchange interaction which lines up the spin in a magnetic material depends on Fe-O-Fe

angle θ, rather it is directly proportional to cosθ. Li3+

doping in Sb3+

site change the structure

and thus bond angle will increase which leads to increase the exchange interaction. This

increase value of exchange interaction aligns the spin more and more and increases the

magnetization. Also Fe3+

substitution by Mo3+

ion breaks down the balanced between the

anti-parallel sub-lattice magnetization of Fe3+

and gives a contribution towards large

magnetization.

4. Conclusion

The new composition of multiferroic SbFeO3 with a general formula material

(SbLi)1/2Fe2/3Mo1/3O3 was prepared. The material is in orthorhombic system with the

crystallite size of 37.63 nm. Complex impedance spectroscopy study stated the contribution

of both grain and grain boundary effect are taken place at all temperature (275-500 ºC).

Impedance study also predicts that the material is non-Debye type. The dc conductivity of the

8

material is followed by Arrhenius-type behavior and the activation energy (275-500 ºC)

calculated from grain and grain boundary effect is 0.60 eV and 0.47 eV respectively. Ac

conductivity is governed by Jonscher’s universal power law. The presence of ferroelectric

hysteresis loop confirms ferroelectric nature of the material. The value of remnant

magnetization (Mr), saturation magnetization (Ms) and coercive field (Hc) are 0.0151 emu/g,

0.31468 emu/g and 646.254 Oe respectively.

References:

1. K.S. Nalwa, A. Garg, A. Upadhyaya, Mater. Letts. 62 (2008) 878-881.

2. G. Anjum, S. mullah, D.K. Shukla, Ravi Kumar, Mater. Letts. 64 (2010) 2003-2005.

3. R. Rai, A. L. Kholkin, Seema Sharma, J. Alloys. Comp. 506 (2010) 815-819.

4. N. Van Minh, N. Gia Quan, J. Alloys Comp. 509 (2011) 2663-2666.

5. Bin Li, C. Wang, W. L., Mao Ye, N. Wang, J. Mat. Letts 90 (2013) 45-48.

6. S. Pattanayak , R.N.P. Choudhary, Piyush R. Das, S.R. Shannigrahi, Ceram. Int 40

(2014) 7983–799.

7. W. Mao, X. Li, Y. Li, X. Wang, Y. Wang, Y. Ma, X. Feng, T. Yang, J. Yang, Mat.

Letts. 97 (2013) 56-58.

8. M.S. Wu, Z.B. Huang, C.X. Han, S.l. Yuan, C.L. Lu, S.C. Xia, Solid State Comm.

152 (2012) 2142-2146.

9. S.K. Bera, S.K. Barik, R.N.P. Choudhary, P.K. Bajpai, Bull. Mater. Sci. 35(1) (2012)

47-51.

10. J. Wu, S. Qiao, J. Wang, D. Xiao, J. Zhu, Appl. Phys. Lett.102, 052904 (2013).

11. J. Wu, J. Wang , Acta Mater. 58 (2010) 1688–1697.

12. POWDMULT: An interactive powder diffraction data interpretations and indexing

Program Version 2.1,E.WU School of Physical Sciences, Flinder University of South

Australia Bradford Park, SA 5042, Australia.

13. F.A. Kroger, H.J. Vink, Solid State Phys. 3 (1956) 307.

14. Ren Chen Da, Yi Guo Yan, Electron. Elem. Mater. 1 (1982) 25.

15. B.K. Barick, K.K. Mishra, A.K. Arora, R.N.P. Choudhary, D.K. Pradhan, J. Phys. D:

Appl. Phys. 44 (2011) 355402–355410.

16. S. Sen, R.N.P. Choudhary, A. Tarafdar, P. Pramanik, J. Appl. Phys. 99 (2006)

124114–124118.

9

17. D.K. Pradhan, R.N.P. Choudhary, C. Rinaldi, R.S. Katiyar, J. Appl. Phys. 106 (2009)

024102–024110.

18. S.S.N. Bharadwaja, S.B. Krupanidhi, J. Appl. Phys. 86 (1999) 5862–5869.

19. C. Tian, S.W. Chan, J. Am. Ceram. Soc. 5 (2002) 2222–2229.

20. B. Pati, R.N.P. Choudhary, P.R. Das, J. Alloys Comp. 579 (2013) 218-226.

21. J. Wu and J. Wang, J. Am. Ceram. Soc. 93 [9] (2010) 2795–2803.

22. J. Wu, J. Wang, D. Xiao, and J. Zhu, J. Appl. Phys.110 (2011) 064104

23. B. Tiwari, R.N.P. Choudhary, J. Phys. Chem. Solids 69 (2008) 2852-2857.

24. A.K. Singh, Subrat K. Barik, R.N.P. Choudhary, P.K. Mahapatra, J. Alloys Comp.

479 (2009) 39-42.

25. R. Rai, S.K. Mishra, N.K. Singh, S. Sharma, A.L. Kholkin, Curr. Appl. Phys. 11

(2011) 508-512.

26. R. Mazumder, A. Sen, J. Alloys Comp. 475 (2009) 577-580.

27. Z.H. Chi, J. Magn. and Magnetic Mater. 310 (2007) 358-360.

28. V.S. Puli, A. Kumar, N. Panwar, I.C. Panwar, R.S. Katiyar, J. Alloys Comp, 509

(2011) 8223-8227.

29. X. Zhang, Yu Sui, X. Wang, Y. Wang, Z. Wang, J. Alloys Comp. 507 (2010) 157-

161.

30. P. Guzdek, M. Sikora, Ł. Góra, Cz. Kapusta J. Eur. Ceram. Soc. 32 (2012) 2007–

2011

31. P. Guzdek , J. Magn. Magn. Mater. 349 (2014) 219–223

32. H.O. Rodrigues, G.F.M.P. Junior, J.S. Almeida, E.O. Sancho, A.C. Ferreira, M.A.S.

Silva, A.S.B. Sombra, J. Phys. Chem. Solids 71 (2010) 1329-1336.

33. D.C. Jia, J.H. Hu, H. Ke, W. Wang, Y. Zhou, J. Euro. Society 29 (2009) 3099-3103.

10

FIGURE CAPTIONS

Fig. 1: Typical thermo gravimetric curve of the un-calcined SLFMO mixture

Fig. 2: Room temperature XRD pattern of the calcined powder of SLFMO

Fig. 3: Nyquist plots of SLFMO at different temperatures

Fig. 4: Equivalent circuit for SLFMO

Fig. 5: Variation of dc conductivity (ζdc) with inverse of temperature

Fig. 6: Variation of ac conductivity (ζac) with frequency at different temperatures

Fig. 7: Polarization hysteresis (P-E) loop of SLFMO at room temperature

Fig. 8: Variation of magnetic moment with applied magnetic field at room temperature

Table 1: Model equivalent circuit fitted parameters Rg (Ohm) and Rgb (Ohm) of SLFMO

Temperature (ºC) Rg() Rgb() Cg(F) Cgb(F) τg (sec) τgb(sec)

275 58020 7029 5.06E-11 1.33E-09 2.93E-06 9.35E-06

300 35190 3133 4.44E-11 5.09E-10 1.56E-06 1.59E-06

325 20060 2992 4.81E-11 2.78E-10 9.64E-07 8.32E-07

350 18050 1980 4.45E-11 1.37E-10 8.03E-07 2.72E-07

375 13850 1406 3.86E-11 1.06E-10 5.34E-07 1.48E-07

400 5654 1142 2.42E-11 1.39E-10 1.37E-07 1.59E-07

425 3755 878 8.61E-12 1.30E-10 3.23E-08 1.14E-07

450 2755 623 5.20E-27 1.26E-10 1.43E-23 7.87E-08

475 1962 459 1.22E-25 1.40E-10 2.39E-22 6.42E-08

500 1407 258 2.98E-21 2.31E-10 4.19E-18 5.98E-08

Fig. 1: Typical thermo gravimetric curve of the un-calcined SLFMO mixture

Fig. 2: Room temperature XRD pattern of the calcined powder of SLFMO

Fig. 3: Nyquist plots of SLFMO at different temperatures

Fig . 4: Equivalent circuit for SLFMO

Fig. 5: Variation of dc conductivity (σdc) with inverse of temperature

Fig. 6: Variation of ac conductivity (σac) with frequency at different temperatures

Fig. 7: Polarization hysteresis (P-E) loop of SLFMO at room temperature

Fig. 8: Variation of magnetic moment with applied magnetic field at room temperature

This paper describes the "Electrical and Magnetic Properties of

(SbLi)1/2Fe2/3Mo1/3O3 Multiferroic Material". The compound has an excellent electrical

and moderate magnetic property.